This invention relates to the determination of engine mass air-flow and more particularly to a method and means for deriving an indication of the mass of air available for combustion within a cylinder of a crankcase scavenged two-stroke engine.
In a crankcase scavenged two-stroke engine, each cylinder has a separate crankcase chamber into which air is inducted during a portion of the engine operating cycle. The inducted air is trapped in the crankcase chamber and then compressed during a part of the engine cycle when the crankcase chamber is decreasing in volume and is then transferred to a combustion chamber where it is mixed with fuel for ignition.
In order to effectively control the emission and performance characteristics of crankcase scavenged two-stroke engines, it is necessary to know the mass of air available at the time of combustion within a cylinder. Once such information is known, critical engine parameters, such as spark advance, fueling requirements, and injector timing, can be adjusted to achieve the desired emission and performance objectives.
Mass air-flow sensors are commercially available, and have been used with internal combustion engines in the past to provide the required information regarding the air mass available for combustion. However, at the present time, mass-air flow sensors with sufficient accuracy are relatively expensive as compared to other sensors used for engine control.
Consequently, a need exists for an alternative technique for deriving an indication of the air mass available for combustion within crankcase scavenged two-stroke engines.